1. Field of the Invention
This invention relates to the purging and pumping of a vacuum chamber, and more particularly to a method of pumping to ultra-high vacuum, a vacuum chamber suitable for use in the manufacture of integrated circuit structures.
2. Description of the Related Art
In the prior art, considerable effort has been devoted to providing ultra-high vacuum capability in thin film processing equipment, for example, for use in the formation of integrated circuit structures on semiconductor wafers. Ultra-high vacuum is important for obtaining and sustaining low levels of contamination during production of the integrated circuit structures. However, in pumping to ultra-high vacuum, for example, when PVD processing is practiced, it is important to minimize the period of time required because such time is non-production time. Further, when testing vacuum chamber equipment for ultra-high vacuum, it is desirable to predict the integrity of the vacuum chamber during the pump to ultra-high vacuum levels to avoid wasted pumping time.
Various methods have been used for purging or decontaminating vacuum systems, including electropolishing, baking at elevated temperatures, photon-stimulated desorption and glow discharge cleaning using oxygen or noble gas. However, these approaches are not without problems. For example, baking is time consuming because a molecule released from a surface in the chamber is not efficiently removed to the chamber exit. Upon release, the desorbed molecule can take what is referred to as a random path where it can strike other surfaces in the chamber with the chance of becoming re-adsorbed. On the other hand, glow discharge cleaning can result in further contamination by absorption of the cleaning gases into the chamber surfaces.
These gases are emitted later which leads to contamination. Also, it has been reported that glow discharge cleaning may not be uniform, particularly in complicated chamber geometry.
Other systems have been reported which can reach ultra-high vacuum in a matter of minutes. Such systems employ expensive mirror finishes to minimize contaminants and water adsorption, glow-discharge cleaning using super-dry nitrogen gas, and double turbomolecular pumps. However, fabrication of such systems is very costly and, accordingly, would be impractical.
Thus, there is a great need for an economical method for purging a vacuum chamber that would permit pumping to an ultra-high vacuum in a relatively short time, thereby ensuring a contaminant-free environment.